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Photosynthesis using light to make food unit 5. Have you thanked a green plant today?

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Presentation on theme: "Photosynthesis using light to make food unit 5. Have you thanked a green plant today?"— Presentation transcript:

1 Photosynthesis using light to make food unit 5

2 Have you thanked a green plant today?

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4 Energy for Life Processes Review: All living things use energy - autotrophs / heterotrophs Review: All living things use energy - autotrophs / heterotrophs Autotrophs- organisms that manufacture their own food. Autotrophs- organisms that manufacture their own food. Most autotrophs use PHOTOSYNTHESIS to obtain food. Most autotrophs use PHOTOSYNTHESIS to obtain food. Besides plants, algae and some bacteria are photosynthetic organisms Besides plants, algae and some bacteria are photosynthetic organisms

5 Energy from food monomers

6 Energy & Chemical Cycling

7 Organisms that photosynthesize

8 Overview - What is the general equation for photosynthesis?

9 Reactants: Tracking atoms in photosynthesis 6 CO 2 Products: 12 H 2 O 6 O 2 6 H 2 O C 6 H 12 O 6 Photosynthesis is a redox process in which H 2 O is oxidized and C O 2 is reduced

10 Today’s Focus: Photosynthesis: process of converting solar energy into chemical energy We can break down photosynthesis into two different stages:  Light-dependent reactions  Light-independent reactions Focus question: How do plants convert solar energy into chemical energy?

11 Photosynthesis 2-part overview

12 Not all plants photosynthesize: parasitic Dodder

13 Where in plants does photosynthesis occur?

14 All green parts of a plant have chloroplasts!

15 zoom into a plant cell inside a chloroplast Chloroplast – is a light absorbing organelle Features inside: GRANA (granum – singular) - stacks of thylakoids. (thigh) STROMA- solution that surrounds thylakoids

16 Chloroplast: sites of photosynthesis

17 In a typical plant cell, what are the different membranes light has to cross to reach chlorophyll? Stop and Jot

18 Beginning of photosynthesis story (Part I the light reactions): Step 1. Light must be absorbed into the chloroplasts. One cell in a plant leaf can have 50 or more chloroplasts. One cell in a plant leaf can have 50 or more chloroplasts. BASICS OF LIGHT BASICS OF LIGHT Sunlight -> white light (really the whole visible spectrum) ROYGBIV Sunlight -> white light (really the whole visible spectrum) ROYGBIV Wavelength Wavelength Pigment - compound that absorbs light Pigment - compound that absorbs light Absorbs, reflects, transmits. Absorbs, reflects, transmits. Absorption spectra Absorption spectra

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20 Thylakoid In membrane - lots of pigments: most imp. pigment -> chlorophylls In membrane - lots of pigments: most imp. pigment -> chlorophylls Accessory pigments - chlorophyll b, carotenoids, etc. Accessory pigments - chlorophyll b, carotenoids, etc. In leaves of plants the chlorophylls are most abundant pigment -> thus leaves green. In leaves of plants the chlorophylls are most abundant pigment -> thus leaves green. In Autumn - lose chlorophylls-> other pigments show through. In Autumn - lose chlorophylls-> other pigments show through. Non-photosynthetic parts of plant? Non-photosynthetic parts of plant?

21 Fig Porphyrin ring: light-absorbing “head” of molecule; note magnesium atom at center in chlorophyll a CH 3 Hydrocarbon tail: interacts with hydrophobic regions of proteins inside thylakoid membranes of chloroplasts; H atoms not shown CHO in chlorophyll b

22 Spectroscopy of Chlorophyll a and b

23 Visible Spectrum

24 Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i +

25 Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2

26 Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2

27 Light Fig H2OH2O Chloroplast Light Reactions NADP + P ADP i + ATP NADPH O2O2 Calvin Cycle CO 2 [CH 2 O] (sugar)

28 The Light Reactions The Light Reactions

29 There are two types of photosystems in the thylakoid membrane Photosystem II (PS II) functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm Photosystem II (PS II) functions first (the numbers reflect order of discovery) and is best at absorbing a wavelength of 680 nm The reaction-center chlorophyll a of PS II is called P680 The reaction-center chlorophyll a of PS II is called P680 Photosystem I (PS I) is best at absorbing a wavelength of 700 nm Photosystem I (PS I) is best at absorbing a wavelength of 700 nm The reaction-center chlorophyll a of PS I is called P700 The reaction-center chlorophyll a of PS I is called P700 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Photosystems: protein complex that contains pigments

30 Chlorophyll pigment is found in the thylakoid membrane How does chloroplast structure relate to its function?

31 Fig THYLAKOID SPACE (INTERIOR OF THYLAKOID) STROMA e–e– Pigment molecules Photon Transfer of energy Special pair of chlorophyll a molecules Thylakoid membrane Photosystem Primary electron acceptor Reaction-center complex Light-harvesting complexes

32 What does the light energy end up doing in photosystem II? A photon hits a pigment and its energy is passed among pigment molecules until it excites P680 A photon hits a pigment and its energy is passed among pigment molecules until it excites P680 An excited electron from P680 is transferred to the primary electron acceptor An excited electron from P680 is transferred to the primary electron acceptor Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Electron Resonance Transfer (excitation energy)

33 © 2010 Pearson Education, Inc. Analyzing models

34 Producing ATP and NADPH

35 Fig Mill makes ATP e–e– NADPH Photon e–e– e–e– e–e– e–e– e–e– ATP Photosystem IIPhotosystem I e–e–

36 Fig Light Fd Cytochrome complex ADP + i H+H+ ATP P synthase To Calvin Cycle STROMA (low H + concentration) Thylakoid membrane THYLAKOID SPACE (high H + concentration) STROMA (low H + concentration) Photosystem II Photosystem I 4 H + Pq Pc Light NADP + reductase NADP + + H + NADPH +2 H + H2OH2O O2O2 e–e– e–e– 1/21/

37 Light reactions happen in the thylakoids Split water Release oxygen Reduce NADP+ to NADPH Generate ATP from ADP by photophosphorylation Summary of light reactions

38 Where does the original high energy electrons come from? What is the final electron acceptor? Check For Understanding

39 Relating cellular respiration to photosynthesis Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP Mitochondria transfer chemical energy from food to ATP; chloroplasts transform light energy into the chemical energy of ATP

40 Part II: The Calvin Cycle uses ATP and NADPH to convert CO 2 to sugar The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle The Calvin cycle, like the citric acid cycle, regenerates its starting material after molecules enter and leave the cycle The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH The cycle builds sugar from smaller molecules by using ATP and the reducing power of electrons carried by NADPH Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

41 Carbon enters the cycle as CO 2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P) Carbon enters the cycle as CO 2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P) For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO 2 For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO 2 The Calvin cycle has three phases: The Calvin cycle has three phases: Carbon fixation (catalyzed by rubisco ) Carbon fixation (catalyzed by rubisco ) Reduction Reduction Regeneration of the CO 2 acceptor (RuBP) Regeneration of the CO 2 acceptor (RuBP) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

42 Fig Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO 2 P P P P P

43 Fig Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO 2 P P P P P ATP 6 6 ADP P P 6 1,3-Bisphosphoglycerate 6 P P NADP + NADPH i Phase 2: Reduction Glyceraldehyde-3-phosphate (G3P) 1 P Output G3P (a sugar) Glucose and other organic compounds Calvin Cycle

44 Fig Ribulose bisphosphate (RuBP) 3-Phosphoglycerate Short-lived intermediate Phase 1: Carbon fixation (Entering one at a time) Rubisco Input CO 2 P P P P P ATP 6 6 ADP P P 6 1,3-Bisphosphoglycerate 6 P P NADP + NADPH i Phase 2: Reduction Glyceraldehyde-3-phosphate (G3P) 1 P Output G3P (a sugar) Glucose and other organic compounds Calvin Cycle 3 3 ADP ATP 5 P Phase 3: Regeneration of the CO 2 acceptor (RuBP) G3P

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46 Fig. 10-UN2 Regeneration of CO 2 acceptor 1 G3P (3C) Reduction Carbon fixation 3 CO 2 Calvin Cycle 6  3C 5  3C 3  5C

47 Fig. 10-UN4

48 You should now be able to: 1.Describe the structure of a chloroplast 2.Trace the movement of electrons in linear electron flow Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

49 Alternative mechanisms

50 Alternative Mechanisms Stomata: absorb CO2 and release water Stomata: absorb CO2 and release water On a hot day, plants close their stomata (reduce the CO2 present) On a hot day, plants close their stomata (reduce the CO2 present)

51 Water Saving Adaptations: C 4 and CAM Plants

52 C4C4C4C4

53 C4

54 CAM

55 CAM Plants: Night and Day

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58 Photorespiration CO 2 becomes scarce CO 2 becomes scarce Rubisco binds to O 2 instead of CO 2 Rubisco binds to O 2 instead of CO 2 ATP consumed rather than generated! ATP consumed rather than generated! No sugar produced! No sugar produced! Consumes organic material from Calvin Cycle! Consumes organic material from Calvin Cycle! What’s the point? What’s the point? In some case clear evidence that photorespiration protects plants from damaging products of light reaction which build up when CO 2 is scarce In some case clear evidence that photorespiration protects plants from damaging products of light reaction which build up when CO 2 is scarce

59 Atmospheric CO 2 Concentrations

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